Macrocyclic oligoesters, also referred to as macrocyclic polyester oligomers (MPOs), have unique physical properties that facilitate the manufacture of polyester products. Macrocyclic oligoesters demonstrate certain processing advantages of thermosets, yet can be polymerized to form thermoplastic polyesters which provide superior toughness, excellent chemical resistance, high heat resistance, and are thermoformable, paintable, bondable, weldable, and recyclable. For example, macrocyclic oligoesters melt into a low viscosity fluid when heated. The low melt viscosity allows the macrocyclic oligoester resin to easily fill molds or permeate fabrics to make prepregs. Furthermore, certain macrocyclic oligoesters melt and polymerize at temperatures well below the melting point of the resulting polymer. Upon melting and in the presence of an appropriate catalyst, polymerization and crystallization can occur virtually isothermally, without significant heat generation and without production of volatile organic compounds (VOCs) or other harmful emissions. The polymerized product can be released without cooling the mold, and the time and expense required to thermally cycle a tool is favorably reduced.
Production of macrocyclic oligoesters such as macrocyclic (1,4-butylene terephthalate) typically involves the use of one or more solvents such as o-dichlorobenzene or xylene. For example, linear polyester can be depolymerized in solvent to form macrocyclic oligoesters. The macrocyclic oligoester product is removed from the solvent, and the isolated macrocyclic oligoester is shaped into a solid form that is easily transportable or that is otherwise amenable to further processing, e.g., polymerization to form a thermoplastic product.
Previous techniques for recovering macrocyclic oligoesters dissolved in a solvent require the addition of a large amount of anti-solvent to the solution to precipitate the macrocyclic oligoester, followed by collection of the product using a filter or a centrifuge. In certain techniques, the solution is also cooled to aid precipitation of the macrocyclic oligoester by reducing its solubility. The use of anti-solvent increases processing complexity, cost, and creates environmental storage and disposal concerns. Furthermore, previous batch operations for manufacturing, isolating, and shaping macrocyclic oligoester product are inefficient because they are only capable of producing limited quantities of macrocyclic oligoester product at a time.
There is a need for effective and efficient methods of isolating and shaping macrocyclic oligoesters, without requiring the use of a large amount of anti-solvent. There is also a need for continuous or semi-continuous processes for isolating and shaping macrocyclic oligoesters in order to improve upon the production efficiency of current batch processes and to lower the cost of producing macrocyclic oligoester product.